1. Field
Embodiments relate to an organic light-emitting display device.
2. Description of the Related Art
Organic light-emitting display devices, which are next-generation display devices having self light-emitting characteristics, have better characteristics than liquid crystal display devices in terms of viewing angle, contrast, response speed, and power consumption. In addition organic light-emitting display devices can be manufactured to be thin and lightweight, since a backlight is not required.
An organic light-emitting display device may include an anode, an organic layer and a cathode stacked sequentially on a substrate having pixel circuits such as thin-film transistors. Types of light emission may largely be divided into a top emission structure or a bottom emission structure according to the direction of light emission. In the top emission structure, an image is realized in a direction in which the organic light-emitting display device is formed, that is, in the direction of the cathode opposite to the direction of the substrate. The top emission structure ensures a higher aperture ratio than the bottom emission structure in which an image is realized in the direction of the substrate. Accordingly, higher light-emitting efficiency can be achieved in the top emission structure.
In the case of the top emission structure, the cathode formed at the top of the organic light-emitting display device must be transparent. However, there is a limit to forming a transparent cathode. That is, as a basic requirement, the cathode must have a lower work function than the anode. However, materials that meet the low work function requirement are mostly materials (such as metal) having low light transmittance. A conventional transparent cathode is formed of a thin film of metal having a low work function. However, since the light transmittance of the conventional transparent cathode is very low, there is a limit to improving light efficiency. Accordingly, various research is being conducted on a method of improving light transmittance.